German Patent Application No. DE 103 20 017 A1 describes control devices for a drive unit which control or regulate the drive unit in particular regarding a drive torque output, the drive unit being an internal combustion engine of a motor vehicle. In this case the motor vehicle normally includes a driver input sensing device operatable by the driver of the motor vehicle, in particular a foot-operatable accelerator pedal which is provided for outputting an output signal representing the instantaneous operating state of the driver input sensing device. A control unit receives the output signal of the driver input sensing device and assigns at least one setpoint output quantity, in particular a setpoint drive torque of the drive unit, to the received output signal. The drive unit is controlled by the control unit in such a way that an actual output quantity output by the drive unit approaches the setpoint output quantity. Such control devices are available in different designs for regular motor vehicle motors, in particular gasoline and diesel engines, for example, Bosch engine control systems having an electronic gas pedal (EGAS).
Furthermore, performing continuous torque monitoring for detecting malfunctions in the control unit is conventional. This is used, in particular, for protecting the vehicle occupants in the motor vehicle and external traffic participants. Unintended acceleration of the vehicle is to be prevented. The core of continuous torque monitoring is the comparison of an actual torque provided by the motor with an allowable torque. In the normal case, the actual torque is less than the allowable torque. If the actual torque exceeds the allowable torque, there is a malfunction in the engine control unit and an error response leading to a safe vehicle state is initiated.
The engine control units are normally monitored according to a three-level monitoring concept. The engine is actually controlled, in particular the setpoint torque is defined, on the first level known as the function level. The second level (monitoring level) is designed as continuous torque monitoring. On this level, an allowable torque is ascertained as a function of vehicle and engine functions, among other things, and compared with an actual engine torque. Level 2 is secured in a complex manner (double storage of all variables, cyclic RAM and ROM check, program sequence check, instruction test). Level 3 is used for securing the computer.
German Patent Application No. DE 102 10 684 A1 describes a method for monitoring a torque of a drive unit of a vehicle. The torque to be monitored is compared to an allowable torque; the allowable torque is adjusted to the torque to be monitored and a malfunction is detected if the torque to be monitored differs from the allowable torque by more than a first predefined value, the malfunction being detected only in the case where a position of an operating control element, in particular an accelerator pedal position, has been within a first predefined tolerance range at least since a first predefined point in time.
German Patent Application No. DE 197 39 565 A1 describes a method for controlling the torque of a drive unit of a motor vehicle in which the torque of the drive unit is set at least according to the driver's input, the actual torque of the drive unit being determined and a maximum allowable torque being ascertained at least on the basis of the driver's input. The torque is reduced and/or limited when the actual torque exceeds the maximum allowable torque. At least one operating state is established in which the torque of the drive unit is increased due to additional load. The maximum allowable torque is increased during this at least one operating state. In particular, the allowable torque is increased during operation with a cold drive unit and/or when operating high-load consumers.
German Patent Application No. DE 197 48 355 A1 describes a method for controlling the drive unit of a vehicle, the torque of the drive unit being predefined as a function of a driver's intended torque derived from the position of an operating control element operatable by the driver and as a function of a setpoint torque which is predefined from at least one external function which influences the toque instead of or in addition to the driver's input. A maximum allowable torque is predefined and, when this maximum allowable value is exceeded, the torque is reduced via the corresponding actual value. The maximum allowable torque is formed at least as a function of the position of the operating control element and the maximum allowable torque is formed as a function of the setpoint torque of the at least one external function if this setpoint torque is greater than the allowable torque which is a function of the position of the operating control element. The external function may increase the torque, for example, with respect to the driver's input as an engine-drag-torque control or a cruise control.
The above-described conventional torque monitoring methods are not applicable to hybrid vehicles in a straightforward manner. In hybrid vehicles, at least one additional torque source (motor) is used in addition to the internal combustion engine. In most cases this is an electric motor.
The intended torque requested by the driver, which is set, for example, by operating an accelerator pedal, must now be divided among the torque sources present (at least two motors) in the engine controller. This is performed as a function of a number of environmental variables, for example, with the purpose of setting the operating point which is the most favorable from the consumption point of view for all torque sources. Such a method is described in German Patent Application No. DE 102 02 531 A1, for example.
So far no conventional torque monitoring concept takes into account the special requirements of such a hybrid drive having one or more electric motors in addition to an internal combustion engine. An additional electric motor connected to the drive train may cause, in the event of an excessive control current, an undesirable vehicle acceleration just as a “simple” internal combustion engine and therefore requires continuous torque monitoring.